# How high does blood sugar have to be to cause eye/nerve/extremity damage? **URL:** \ **Category:** Factual Questions\ **Created:** [May 28, 2015, 5:14am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017 "2015-05-28T05:14:59Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [May 28, 2015, 5:14am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/1 "2015-05-28T05:14:59Z")
How high does blood sugar have to be to cause eye/nerve/extremity damage? Would it be, say, a fasting 6.5 A1C or 100 blood glucose for several months? Ballpark figures are fine. ---
**Author:** ![Terr](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@Terr](https://boards.straightdope.com/u/Terr)\ **Post date:** [May 28, 2015, 5:20am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/2 "2015-05-28T05:20:12Z")
> [@Velocity](#): > > Would it be, say, a fasting 6.5 A1C or 100 blood glucose for several months? Ballpark figures are fine. ??? 6.5 A1C and 100 fasting blood glucose is stellar for a diabetic. ---
**Author:** ![Skald\_the\_Rhymer](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Skald\_the\_Rhymer](https://boards.straightdope.com/u/Skald_the_Rhymer)\ **Post date:** [May 28, 2015, 5:23am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/3 "2015-05-28T05:23:10Z")
Fasting A1C makes no sense to me. A1C is a measure of blood glucose levels over several months, not at a particular moment. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [May 28, 2015, 5:45am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/4 "2015-05-28T05:45:08Z")
> [@Skald\_the\_Rhymer](#): > > Fasting A1C makes no sense to me. A1C is a measure of blood glucose levels over several months, not at a particular moment. Ooops you’re right! Fasting blood sugar. A1C is A1C. ---
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [May 28, 2015, 6:00am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/5 "2015-05-28T06:00:10Z")
I think probably you would be talking years for damage to occur. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 28, 2015, 9:37am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/6 "2015-05-28T09:37:22Z")
I don’t have time to search now, but we had this discussion in the last 4 months. Some digging out to locate the thread easily. There were some good cites given that numbers \*around there \*are negligible risk. But don’t forget, 6.0 to 6.5 to 7.0 are big differences in A1C. And any given test run is only accurate +/- 0.5 ish. So if your 6.5 is really a 6 you’d be fine for decades, but if it’s really a 7 you’d expect beginning signs of deterioration in a few years at most. The big unknowable is whether your 6.5 today turns into 7.5 in 2 years or in 20. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [May 28, 2015, 10:46am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/7 "2015-05-28T10:46:43Z")
> [@LSLGuy](#): > > I don’t have time to search now, but we had this discussion in the last 4 months. Some digging out to locate the thread easily. > > There were some good cites given that numbers \*around there \*are negligible risk. > > But don’t forget, 6.0 to 6.5 to 7.0 are big differences in A1C. And any given test run is only accurate +/- 0.5 ish. So if your 6.5 is really a 6 you’d be fine for decades, but if it’s really a 7 you’d expect beginning signs of deterioration in a few years at most. > > The big unknowable is whether your 6.5 today turns into 7.5 in 2 years or in 20. I hope I’m not jus whistling in the dark here, but I thought 7 was tolerable and, in fact, was the just-made-it line until fairly recently. (Me 7.1.) ---
**Author:** ![lieu](https://avatars.discourse-cdn.com/v4/letter/l/c2a13f/32.png) [@lieu](https://boards.straightdope.com/u/lieu)\ **Post date:** [May 28, 2015, 11:37am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/8 "2015-05-28T11:37:48Z")
> [@LSLGuy](#): > > I don’t have time to search now, but we had this discussion in the last 4 months. Some digging out to locate the thread easily. There was a good thread on “peripheral neuropathy” that may be of some help. ---
**Author:** ![purplehorseshoe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/purplehorseshoe/32/2996_2.png) [@purplehorseshoe](https://boards.straightdope.com/u/purplehorseshoe)\ **Post date:** [May 28, 2015, 1:38pm UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/9 "2015-05-28T13:38:26Z")
Is it too much of a hijack to ask for a nutshell summary of the “how/why” of the damage? What’s the mechanism where sugar in blood → cellular damage? Again, if I should wander off to one of the afore-mentioned previous threads, please feel free to let me know. 🙂 ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [May 28, 2015, 1:44pm UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/10 "2015-05-28T13:44:23Z")
> [@purplehorseshoe](#): > > Is it too much of a hijack to ask for a nutshell summary of the “how/why” of the damage? What’s the mechanism where sugar in blood –\> cellular damage? > > Again, if I should wander off to one of the afore-mentioned previous threads, please feel free to let me know. 🙂 Imagine there’s a hole in the fill pipe to the gas tank of your car, and if you overfill it, the extra gas spills into the trunk. Generally hard on the things in the trunk, and if any of the bodies back there has a still-lit pipe in his pocket, this could be very bad. As the trunk gets filled more and more, the fumes eventually work their way out into the passenger compartment, and that’s generally very bad. In terms of the body, too much glucose has some sort of abrasive effect on all the small blood vessels, whether they’re in your eyes, the tips of your toes & fingers, etc. The smallest blood vessels supply blood to the nerves in these areas, so disrupting the blood vessels (and the flow of blood) causes the nerves to not work so well. ---
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [May 28, 2015, 2:25pm UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/11 "2015-05-28T14:25:43Z")
[![](https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQKf_AofdIjhppBazfWvhnKT8KLoV3QoLDIb0Vf59RKKxGmtzQj3MZKdzk) ](https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQKf_AofdIjhppBazfWvhnKT8KLoV3QoLDIb0Vf59RKKxGmtzQj3MZKdzk) ---
**Author:** ![Surreal](https://avatars.discourse-cdn.com/v4/letter/s/eada6e/32.png) [@Surreal](https://boards.straightdope.com/u/Surreal)\ **Post date:** [May 28, 2015, 3:50pm UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/12 "2015-05-28T15:50:37Z")
> [@Leo\_Bloom](#): > > I hope I’m not jus whistling in the dark here, but I thought 7 was tolerable and, in fact, was the just-made-it line until fairly recently. (Me 7.1.) > **[Association of glycaemia with macrovascular and microvascular complications...](https://www.bmj.com/content/321/7258/405.abstract)** > > Objective: To determine the relation between exposure to glycaemia over time and the risk of macrovascular or microvascular complications in patients with type 2 diabetes. > > Design: Prospective observational study. > > Setting: 23 hospital based clinics... > [@](#): > > Objective: To determine the relation between exposure to glycaemia over time and the risk of macrovascular or microvascular complications in patients with type 2 diabetes. > > Design: Prospective observational study. > > Setting: 23 hospital based clinics in England, Scotland, and Northern Ireland. > > Participants: 4585 white, Asian Indian, and Afro-Caribbean UKPDS patients, whether randomised or not to treatment, were included in analyses of incidence; of these, 3642 were included in analyses of relative risk. > > Outcome measures: Primary predefined aggregate clinical outcomes: any end point or deaths related to diabetes and all cause mortality. Secondary aggregate outcomes: myocardial infarction, stroke, amputation (including death from peripheral vascular disease), and microvascular disease (predominantly retinal photo-coagulation). Single end points: non-fatal heart failure and cataract extraction. Risk reduction associated with a 1% reduction in updated mean HbA1c adjusted for possible confounders at diagnosis of diabetes. > > Results: The incidence of clinical complications was significantly associated with glycaemia. **Each 1% reduction in updated mean HbA1c was associated with reductions in risk of 21% for any end point related to diabetes (95% confidence interval 17% to 24%, P\<0.0001), 21% for deaths related to diabetes (15% to 27%, P\<0.0001), 14% for myocardial infarction (8% to 21%, P\<0.0001), and 37% for microvascular complications (33% to 41%, P\<0.0001). No threshold of risk was observed for any end point.** > > Conclusions: In patients with type 2 diabetes the risk of diabetic complications was strongly associated with previous hyperglycaemia. **Any reduction in HbA1c is likely to reduce the risk of complications, with the lowest risk being in those with HbA1c values in the normal range (\<6.0%).** ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [May 28, 2015, 4:56pm UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/13 "2015-05-28T16:56:02Z")
Nevertheless the risk and consequences of hypoglycemia make the tight control target [more like](http://care.diabetesjournals.org/content/26/suppl_1/s25.full) 7.2: > [@](#): > > … a reasonable goal is the mean plasma glucose and HbAlc levels achieved in the intensive treatment group of the trial (i.e., mean blood glucose of 155 mg/dl [8.6 mmol/l] and HbAlc of ∼7.2% … The major danger is hypoglycemia, especially in people with type 1 diabetes. Serious hypoglycemia may result in altered consciousness, coma, or convulsions resulting in injury to the patient or others. … The intensive treatment group in the DCCT had a threefold greater risk of severe hypoglycemia than the standard treatment group. … ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 28, 2015, 5:22pm UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/14 "2015-05-28T17:22:28Z")
> [@purplehorseshoe](#): > > Is it too much of a hijack to ask for a nutshell summary of the “how/why” of the damage? What’s the mechanism where sugar in blood –\> cellular damage? > > Again, if I should wander off to one of the afore-mentioned previous threads, please feel free to let me know. 🙂 IN addition to the microvascular issues \*\*Ethelrist \*\*mentioned, high glucose levels promote atherosclerosis. So compared to serotypical folks, more plaque builds up in diabetics’ blood vessels, eventually leading towards heart disease, heart attacks, etc. This is the acute off- ramp for diabetic mortality. The fact diabetes also tends to exacerbate blood cholesterol regulation means diabetics tend to have more of the raw ingredients of atherosclerotic plaques floating around in their blood as well. There are a lot of synergetic reactions going on in there, and they all lead towards worse overall outcomes. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 28, 2015, 8:23pm UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/15 "2015-05-28T20:23:59Z")
> [@DSeid](#): > > Nevertheless the risk and consequences of hypoglycemia make the tight control target [more like](http://care.diabetesjournals.org/content/26/suppl_1/s25.full) 7.2: You are by far the pro here; I’m a gibbering idiot spectator by comparison. So a question if I may … IMO … I’ve seen that study and other similar ones quoted a bunch. What they seem to be saying is that since _hypo_glycemic events can be promptly crippling or fatal, they’re willing, from a statistical perspective, to accept greater A1Cs & more long-term damage to keep folks away from the prompt risks of acute hypoglycemic episodes. Which may very well be a very valid tradeoff on a public health statistical basis, but may not make sense on an individual basis. My thinking goes like this: There are some diabetics who need insulin or other medications that make hypoglycemia a very real risk. Or folks whose overall health, mental condition, or diabetes management skills are flaky enough that acute hypoglycemia is a real risk. For those folks, it makes complete sense to carefully walk the line between acute hypo- and chronic hyper-glycemia. And thereby to accept considerable chronic hyper- to avoid the acute hypo-. IMO, there is another class of diabetics who, due to lesser severity of disease, different drug regimen, better management skills, etc., have essentially zero risk of acute hypoglycemic events. And, ITSM that for that group, there is zero advantage to accepting high A1C and chronic hyperglycemia. IMO, those folks’ goals ought to be minimum A1C, and minimum severity and time of post-meal elevated BG. Ideally this group could diet, exercise, and medicate to normal or near normal daily blood glucose profiles. And be totally safe from hypoglycemia in doing so. And thereby achieve normal or near-normal diabetic comorbidity / co-mortality. The challenge, IMO, is that there aren’t studies which treat these two patient groups separately. And so the standard advice which is doubtless helpful to the first group is (IMO) harmful to the second group. That may be because the second group is a figment of my imagination. Or it may be that there’s really not a clear dividing line between them and the acute hypo risk group. Or maybe even because all the studies are ignoring these folks as not really ill enough to worry about. IOW, they’re not thought to be much of a public health issue at all. Finally, this last group may be healthy enough that it’s hard to design a study sensitive enough to detect the difference in outcomes over a short enough term to be practical. Given all the above surmise, does anyone have any relevant info to add or subtract? Any research support for (or stake through the heart of) my theory? ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [May 28, 2015, 10:44pm UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/16 "2015-05-28T22:44:51Z")
Purely an anecdote, but here goes: The correlation between being excellent at diabetic management and avoiding hypoglycemia is not absolute. My spouse has a form of diabetes that makes _hypo_glycemia more likely than most with Type II. Even though he has had excellent A1C’s, lost 40 pounds and kept it off for nearly a decade, improved his triglyceride numbers, and basically has done everything correctly for many years he is STILL more prone to hypoglycemia than most with Type II. He deals with it by being very observant and getting something to eat as soon as he shows any sign of blood sugar that’s too low. So sometimes you’re just out of luck. Remember, the whole reason someone has diabetes in the first place is because a production/regulation system is malfunctioning. Depending on which part of the system is broken you might well get someone completely compliant with medical directives, medication, diet, and everything else but still having terrible problems. And, indeed, there is a term for those people: “brittle diabetics”. ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [May 28, 2015, 11:17pm UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/17 "2015-05-28T23:17:26Z")
Getting A1C to 7 or below is the goal of a Type II Diabetic, such as me. I’m lucky in that I was able to bring it down from my initial (on diagnosis) 12.8 result to the last couple of years all being between 6.2 and 6.8. I got home from work and ate about 7 ounces of blueberries (yum!) and just now tested my blood sugar at 112. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [May 29, 2015, 12:36am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/18 "2015-05-29T00:36:25Z")
I suffered peripheral neuropathy at least 7 or 8 years before my glucose rose above 7 mmole/l (126 mg/dl) and my A1C was mostly below 6%. And my fasting glucose is now below 6 and the A1C is about 5.5% and the neuropathy is getting worse all the time. A neurologist told me this is not at all unusual. ---
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [May 29, 2015, 1:19am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/19 "2015-05-29T01:19:39Z")
> [@Wesley\_Clark](#): > > [https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQKf\_AofdIjhppBazfWvhnKT8KLoV3QoLDIb0Vf59RKKxGmtzQj3MZKdzk](https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQKf_AofdIjhppBazfWvhnKT8KLoV3QoLDIb0Vf59RKKxGmtzQj3MZKdzk) That is a crappy chart. [http://www.ladalife.com/wp-content/uploads/2013/04/chart-professional-about-a1c-risk.gif](http://www.ladalife.com/wp-content/uploads/2013/04/chart-professional-about-a1c-risk.gif) The risk of eye damage is about 20x higher with an a1c of 12 vs 6. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [May 29, 2015, 1:31am UTC](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017/20 "2015-05-29T01:31:54Z")
> [@LSLGuy](#): > > … What they seem to be saying is that since _hypo_glycemic events can be promptly crippling or fatal, they’re willing, from a statistical perspective, to accept greater A1Cs & more long-term damage to keep folks away from the prompt risks of acute hypoglycemic episodes. > > Which may very well be a very valid tradeoff on a public health statistical basis, but may not make sense on an individual basis. … Oh you are very right, and such was recognized in the link I provided, as can be seen by putting the quote I excerpted in a broader context: > [@](#): > > It appears that there is a direct relationship between blood glucose level and the risk of complications. However, there are other factors, such as genetics, that influence complications. Nevertheless, patients should aim for the best level of glucose control they can achieve without placing themselves at undue risk for hypoglycemia or other hazards associated with tight control … therapy for diabetes must be individualized in consultation between patient and primary health care provider. If the type 1 diabetic patient is intellectually, emotionally, physically, and financially able to attempt tight control, and if a health care team is available to provide resources, guidance, and support, a reasonable goal is the mean plasma glucose and HbAlc levels achieved in the intensive treatment group of the trial (i.e., mean blood glucose of 155 mg/dl [8.6 mmol/l] and HbAlc of ∼7.2% … > > … Tight control should not be attempted by patients unable or unwilling to participate actively in their glucose management. Tight control is contraindicated in infants \<2 years of age. It should be undertaken with extreme caution in children between the ages of 2 and 7 years because hypoglycemia may impair normal brain development, which is not complete until 7 years of age. The danger of hypoglycemia is greater in infants and children because food intake, activity, and adherence to treatment schedules are less predictable than in adults. Because preadolescents appear to be relatively protected from microvascular complications, the need for tight control might be less than in postpubertal subjects. Older patients with significant atherosclerosis may be vulnerable to permanent injury from hypoglycemia. Although there are few absolute contraindications to tight control, relative contraindications will be more frequent. Clinical judgment and common sense will be required in decision making under the latter circumstance. … > > … susceptibility to complications and damage from elevated blood glucose levels is influenced by one’s genes. Unfortunately, we have not identified markers of susceptibility. … [Next page](https://boards.straightdope.com/t/how-high-does-blood-sugar-have-to-be-to-cause-eye-nerve-extremity-damage/721017.md?page=2)